1. Field of the Invention
This invention relates to a method for reducing the population of dust mites by contacting salt crystals on substrates inhabited by dust mites.
2. Background of the Invention
It has been known for many years that common house dust is an important cause of asthma, rhinitis and eczema in allergic individuals. The mite Dermatophygoides pteronyssinus has been identified as a major source of house dust allergen. This mite and the related mites D. farinae, D. microceras and Euroglyphus maynei are the predominant house dust mites in temperate climates in countries including the United States and Europe.
Dust Mites are not insects, but are eight-legged arachnids, relatives of ticks and spiders. They live in close association with humans (or other mammals), their main food source being the shed scales from skin. Adult mites are approximately 300 microns (3/10 mm) in size, having developed over approximately 25 days through egg, larval and nymph stages. Adults live for 2 to 31/2 months, during which time each female can produce about 20-40 eggs. Dust mites are photophobic, living deep in pillows, mattresses, carpets, upholstered furniture and other soft materials.
In addition to a food source, the other essential requirement for dust mite growth is adequate humidity. Dust mites are 75% water by weight. They do not drink water, but must absorb water vapor from the air in order to survive. Specialized glands above their first pair of legs produce secretions high in sodium and potassium chloride, which act to absorb water vapor from surrounding air. This can only be accomplished if the surrounding humidity is sufficiently high. Relative humidities of about 70-75% are optimal for dust mite growth. Dust mites will die at humidities of 50% or less. In geographical areas where humidity is high, dust mites are present in nearly all homes and may be as plentiful as 18,000 mites per gram of dust. Literally millions of mites can inhibit a single bed or carpet.
About ten years ago, it was demonstrated that a major dust mite allergen was present in mite fecal particles. Each mite produces about 20 fecal particles per day, and more than 100,000 of them may be present in a gram of dust. These fecal particles vary from about 10 to 40 microns in size, comparable to the size of pollen grains, and become airborne during domestic activity such as making beds and vacuuming carpets. The chemical structure of mite allergens has been defined, including that of other allergens which are present both on mite bodies and fecal particles.
Acute exposure to mite allergens has been shown to provoke wheezing, rhinitis, eustacian tube obstruction or eczema in sensitized patients. Chronic exposure can cause bronchial hyper-reactivity and chronic asthma. There is a correlation between the level of exposure to house dust mite allergen in early childhood and the likelihood of the subsequent development of asthma. Conversely, asthmatics sensitive to dust mites improve in environments without mites, such as at high altitudes or in hospital rooms. Attempts have therefore been made to decrease patients' exposure to dust mites in the home.
Studies of dust avoidance measures in homes have shown that the use of impermeable mattress and pillow encasings and the removal of bedroom carpeting are associated with a decrease in mite counts. These measures have also been shown to be of clinical value, with a decrease in symptoms and medication requirements occurring in children and adults with dust-sensitive asthma when pillows and mattresses are encased and carpets are removed.
Although carpets and upholstered furniture are major sites of dust mite growth, many allergic individuals are unable or unwilling to remove these from their home. Vacuuming does not remove dust mites or significantly decrease dust mite allergen levels, and in fact, vacuuming of carpets actually increases the amount of airborne dust. It is thus not surprising that trials employing vacuuming rather than removal of carpets failed to produce clinical improvement.
Because of the importance of carpets and textile materials as habitats of dust mites, various chemical acaricides have been proposed to kill mites in those locations.
U.S. Pat. No. 4,666,940 to Bischoff et al discloses an acaricidal composition whose active ingredient is benzyl benzoate. The acaricidal substance is said to be applicable in the form of a liquid, a foam, or as a semi-aqueous pulverulent cleanser. The particle sizes of the residue after application and drying range from about 2 to 100 microns, which is said to be a suitable size range for oral ingestion by dust mites.
Other chemical agents which have been used to kill dust mites include primiphos methyl, natamycin, bioallethrin, deltamethrin and methoprene. These organic compounds may be expensive, and many of them have caused skin, eye or bronchial irritation. They also have the potential to cause allergic or other adverse reactions. The use of such organic compounds in households is therefore not the ideal solution to the problem of reducing the population of dust mites. Liquid nitrogen has been used to kill dust mites in carpets by freezing, but use of liquid nitrogen is potentially dangerous and it must therefore be applied only by a trained technician. An alternative approach is the use of tannic acid, which denatures dust mite antigen but which does not kill the dust mites themselves.
U.S. Pat. No. 3,973,011 to Bohner et al discloses organic oxadiazolyl compounds which are said to be effective pesticides against animal and plant pests. The oxadiazolyl compounds can be used alone or in combination with dispersants, such as alkali salts.
U.S. Pat. No. 1,767,528 to Jones discloses a cleaning and disinfecting compound designed for household use, which contains common salt. U.S. Pat. Nos. 1,576,105 and 1,576,106 both to Fetherston disclose the use of sodium chloride for controlling the proliferation of microbes in garbage containers to reduce odors and other problems associated with decomposing garbage.
U.S. Pat. No. 2,299,604 to Weirich relates to antimycotics containing sodium chloride for controlling athlete's foot. U.S. Pat. No. 191,476 to Seligman discloses a compound for disinfecting and deodorizing horse stables, which contains mineral salts such as potassium carbonate or potassium hydroxide.
U.S. Pat. No. 088,300 to Jaycox discloses a flea powder which includes 25% abstract of Mentha pulegium (a plant commonly known as pennyroyal), 30% snuff, 20% Sinapis (a mustard) and 25% salt. The components are ground individually then uniformly mixed into a powder. Jaycox discloses that the degree of fineness of the ground components is immaterial in using the composition to destroy fleas.
It should be noted that dust mites are as far removed from fleas, as human beings are from turtles.
To be effective in reducing the population of dust mites, acaricidal compounds should be contacted on various substrates which accumulate mites, such as carpets, rugs, bedding materials, such as mattresses, blankets, bedspreads and pillows, upholstered furnishings and toys made from various fabrics, especially stuffed animals. Obviously, the acaricidal substances must not be allergens or irritants to persons coming into close proximity with such substrates, and who are allergic to house dust.
The present invention uses common salt or its substitutes as inexpensive, environmentally safe acaricides.